1. Field of the Invention
The present disclosure relates to a dispersant for carbon nanotubes. In particular, this disclosure relates to a dispersant that promotes excellent dispersion of carbon nanotubes in a composition.
2. Description of the Related Art
Carbon nanotubes (CNT) are tubular molecules in which one carbon atom is bonded with other carbon atoms in a honeycomb arrangement. Carbon nanotubes generally can have a single wall (single wall carbon nanotubes) or multiple walls (multi-wall). Single wall carbon nanotubes have diameters of about 0.7 to about 3 nanometers, while multiwall carbon nanotubes have diameters of about 3.5 to about 500 nanometers. Carbon nanotubes generally have aspect ratios of about 5 to about 10,000. Single wall carbon nanotubes generally exist in the form of ropes due to Vander Waals forces. Carbon nanotubes also exist in the form of bundles called aggregates.
Carbon nanotubes have excellent mechanical properties, high electrical selectivity, excellent field emission properties, and high-efficiency hydrogen storage medium characteristics. Further, carbon nanotubes can exhibit either semiconducting or metallic properties. These various types of carbon nanotubes have different energy gaps and exhibit a peculiar quantum effect because they have a quasi-one-dimensional structure.
Various methods can be used to produce carbon nanotubes such as an electric discharge method, a pyrolysis method, a laser deposition method, a plasma chemical vapor deposition method, a thermal chemical vapor deposition method and an electrolysis method.
Further, since carbon nanotubes have high electrical conductivity, they are used for forming conductive films, and the likelihood that carbon nanotubes will be used in various functional complexes, such as probes of a field emission display (FED) and a scanning probe microscope (SPM), or the like, in the future is increasing. Accordingly, research on carbon nanotubes is increasing feverishly.
Meanwhile, in order to form a conductive film using carbon nanotubes or to apply carbon nanotubes to functional complexes, it is desired that the carbon nanotubes be dispersed in a suitable dispersion medium. However, since carbon nanotubes have a very large surface attractive forces, such as the van der Waals force, which is the force between molecules, carbon nanotube particles easily aggregate with each other to form ropes. This aggregation phenomenon hinders the formation of a three-dimensional structure, which can improve the mechanical strength and conductivity thereof. Accordingly, in order to increase the applicability of carbon nanotubes, technologies for dispersing carbon nanotubes using a suitable dispersant are desired. However, currently, the application of carbon nanotubes is limited due to the ineffectiveness of these dispersion technologies.
A dispersant, which is a kind of surfactant, includes a head and a tail. Here, it is desirable for the head to have an affinity for a dispersoid (e.g., the nanotubes), which is the material to be dispersed, and it is desirable for the tail to have an affinity for a dispersion medium, which is a solvent for dispersing materials. Moreover, it is desirable for a good dispersant to also serve as a barrier for the collision between particles.
Water-based dispersants, such as sodium dodecyl benzene sulfonate (NaDDBS), sodium dodecyl sulfonate, TX-100, polyvinyl pyrrolidone and the like, are used as conventional dispersants for carbon nanotubes. However, there is a problem in that water-based dispersants can easily disperse carbon nanotubes only in water, but cannot effect the dispersing of the carbon nanotubes in an organic solvent.
Further, organic dispersants are not widely known yet. However, Korean Unexamined Application Publication No. 2004-0039425 and Japanese Unexamined Application Publication No. 2004-339301 have disclosed the fact that carbon nanotubes can be easily dispersed in an organic solvent using a polythiophene conjugated polymer. However, the use of a polythiophene polymer has drawbacks, not the least of which is the lack of control over the molecular weight of the polythiophene. The lack of control over the molecular weight causes limited dispersion of the carbon nanotubes in only two or three types of media.
Accordingly, it is desirable to have a dispersant to disperse carbon nanotubes in various solvents, including organic solvents, water-based solvents, and mixtures thereof.